For trendy décor, the writing's on the carpet

In redecorating the Oval Office, Barack Obama has chosen a carpet with slogans round the edge. One is: "The arc of the moral universe is long, but it bends towards justice."

I've never quite understood that. Is a long arc good or bad? The source is a speech that Martin Luther King made on August 18, 1967. It was on the text: "Where do we go from here?" That question might be even more suitable for an Oval Office carpet, but it could give visitors the wrong impression – or even worse, the right one.

I don't know about you, but I had never considered words on my carpets. Where will it all end? Garage doors with: "Open the gates of new life" (Browning)? A chair with: "Sit thou still when kings are arming" (Scott)? A loo with: "Roses for the flush of youth" (Christina Rossetti)?

The itch to cover personal items with written declarations broke out over the chests of a whole civilisation when T-shirts became message-boards. Sometimes, they provide habitat for unwanted jokes: "Work is cutting into my drinking time." Some proclaim more or less noteworthy opinions "Animals taste good." Others ask for trouble: "I hear voices and they don't like you."

Irma Kurtz in The Great American Bus Ride, her alarming book about travelling by public transport, identifies messages on T-shirts as symptoms of a national neurosis. Now it has got into the White House.

It is not that household goods have been quite free from writing. "Bathmat" it says, in a gnomic kind of self-reference, on some bathmats. "Bread" it says on some breadboards, though never "Board". The next step is the "Welcome" on the doormat.

In private houses, such messages to third parties seldom get past the liminal territory of the threshold. In grand public buildings, there may be some general declaration in the first space that visitors come to, traditionally in a dead language.

This kind of lapidary showing-off lends itself to ridicule. The floor of the lobby at Rhodes House, Oxford, bears a Greek inscription that turns out to say "No smoking". A bench by the Cherwell nearby is inscribed: "Ore stabit fortis arare placet ore stat." The joke is the division of the words, which read more plainly as: "O rest a bit for 'tis a rare place to rest at."

You'd expect the joke to wear off if it was on your own furnishings, yet this sort of thing is seeping in to the most careful homes. The rule is that it starts with the least formal items. You wouldn't expect a T-shirt joke on a Wedgwood dinner service. But it is past the outer defences already. Peter Jones, the smart store at Sloane Square, sells teapots bearing the words "More tea, vicar?"

Before, it had sold mugs with "Coffee" on the side, in traditional "Bathmat" convention, and cups with the words: "Hot chocolate." This raises a question: is it right to drink tea out of such a cup, or would it somehow affect the taste? Anyway, the range now extends to a biscuit barrel upon the lid of which, in serifed capitals, appear the words: "Cookies are fab." Tut.

The reason mugs acted as the Trojan horse for such ceramic glossolalia is that they belong to two worlds. Unlike the Wedgwood, they can go outside, to be used by people in T-shirts doing dirty jobs, and it doesn't matter all that much if they are broken. One of the turning points in the decline of Britain came when tea at the office began to be taken from mugs instead of cups and saucers. With the mugs came the slogans.

Last year, for Christmas my grateful team gave me a mug with the wartime motto: "Keep calm and carry on." At least, I assumed gratitude was their motive.

It could have been worse. There are mugs for sale online saying: "Better to remain silent and be thought a fool than to speak out and remove all doubt – Abraham Lincoln", though it doesn't sound like Lincoln to me. Perhaps Mr Obama has it on his tooth-mug.